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GGJJTT Vol. 1, No. 1, September, 2016
Recycling Blends of Rice Husk Ash and Snail Shells as Partial
Replacement for Portland Cement in Building Block Production*
1 E. Nkrumah and 1J. R. Dankwah 1University of Mines and Technology, P.O. Box 237, Tarkwa, Ghana
Nkrumah, E. and Dankwah, J. R. (2016), “Recycling Blends of Rice Husk Ash and Snail Shells as Partial
Replacement for Portland Cement in Building Block Production”, Ghana Journal of Technology, Vol. 1, No. 1,
pp. 67 - 74.
Abstract
This project was experimentally carried out to investigate the effect of a blend of Rice Husk Ash (RHA) and
Calcined Snail Shells (CSS) as a partial replacement for Ordinary Portland Cement (OPC) on the formation of
building blocks in the absence of chemical activation. A total of 24 building blocks of size 100 mm x 70 mm x
50 mm with different percentages by weight of a blend of 20 % RHA and 80 % CSS were used for the
investigation. The percentage partial replacement of OPC was in the order of 0 %, 5 %, 10 %, 15 %, 20 %, 25
%, 30 % and 50 %. A ratio of one part of cement to three parts of sand was used to form the blocks. The blocks
were tested at age 7 and 14 days for compressive strength. Test results indicated that the blocks formed were
above the standard compressive strength of 3.5 N/ according to American Society for Testing of Materials
(ASTM). Compressive strength of the blocks also increases with age of curing and generally decreases as the
percentage of RHA and CSS content increases. The study arrived at an optimum replacement level of 25 % of
cement in forming the building blocks.
Keywords: Rice Husk Ash, Calcined Snail Shell, Ordinary Portland Cement, Building Blocks
1 Introduction
Cement is the most expensive binding material in
block making. Owing to the important role the
cement industry plays in infrastructural
development, affordable housing can be achieved if
multiple efforts are made towards reducing the cost
of production of Portland cement, reduce the
consumption of raw materials for cement
production as well as protect the environment. One
way is to use suitable low-cost, sustainable and
environmentally friendly materials as alternative
binder or admixtures (Ettu et al., 2013). The search
for alternative binder or cement replacement
materials has led to the discovery of the potentials
of using industrial and agricultural by-products,
otherwise regarded as wastes in technologically
disadvantaged communities as cementitious
materials (Raheem and Adesanya, 2011). If these
materials have pozzolanic properties, they impart
technical advantages to the resulting block and also
enable larger quantities of cement replacement to
be achieved.
Due to increasing industrial and agricultural
activities, tonnes of waste materials are deposited
in the environment with little effective method of
waste management or recycling. Some of these
deposits are not easily decomposed and their
accumulation is a threat to the environment and
people at large. These waste materials include rice
husks, maize cobs, snail shells, palm-kennel shell,
coconut shell, saw dust, groundnut shell etc. Global
pollution coupled with resource depletion has
challenged many researchers and engineers to seek
locally available materials with a view to
investigating their usefulness wholly as a
construction material or partly as a substitute for
conventional ones in concrete and block making. In
search for new cost effective and more efficient
materials which address these issues, pozzolana
attracts much interest (Raheem et al., 2013).
The need to reduce the high cost of Ordinary
Portland Cement in order to provide
accommodation for the populace has also
intensified research into the use of some available
materials that could be used as partial replacement
locally for Ordinary Portland Cement (OPC) in
civil engineering and building works (Bakar et al.,
2010). Significant achievements have been made in
this regard and the subject is attracting attention
due to its functional benefit of waste reusability
and sustainable development, reduction in
construction costs and its indigenous technology
and equipment requirements. This also promotes
waste management and recycling at minimal cost,
reduce pollution by the waste and increase the
economic base of the farmer.
Rice Husk Ash (RHA) from parboiling plants and
snail shell pose environmental threat and ways are
being thought of to dispose them (Akeke et al.,
2013). Rice husk and snail shell constitute an
environmental nuisance as they form refuse heaps
*Manuscript received August 23, 2016
Revised version accepted September 16, 2016
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GGJJTT Vol. 1, No. 1, September, 2016
in the areas where they are disposed. The use of
RHA and CSS as a partial replacement for cement
will provide an economic use of the by – product
and consequently produce cheaper blocks for low
cost building (Oyetola and Abdullahi, 2006). The
compressive strength of blocks is considered one of
the most important properties in the hardened state.
For the purpose of structural design, the
compressive strength is the criterion of quality for
building blocks (Umoh and Olusola, 2012)
Extensive compressive strength tests and
workability tests on RHA indicate that it can be
used to substitute for Portland cement at up to 25%
in the manufacture of concrete with no loss in
workability or strength (Muga et al., 2005, Akeke
et al., 2013b). Also, the mechanical performances
of blended cements produced from raw materials
(pozzolana) have revealed that the rate of strength
development and compressive strength at a
particular curing time decrease with increasing
pozzolana content (20-35 %) of blended cements.
Therefore, it was deduced that the raw material up
to 30 % can be added to produce blended cements
of the desired quality for mortar to make block
(Alp et al., 2009).
Oyetola and Abdullahi (2006) observed that lower
percentage replacement level (of between 10 % and
20 % of RHA) ensures that silica from the
pozzolana is in required amount which aids the
hydration process to produce blocks with high
compressive strength. However, in higher
percentage replacement of 30 %, 40 % and 50 %
RHA, the amount of rice husk ash in the mix is
higher than the amount required to combine with
liberated calcium hydroxide during hydration. Thus
excess silica substitute part of the cementitious
material and consequently causes a reduction in
strength. Therefore the need to mix RHA with
calcined snail shell ash for improved compressive
strength of the blocks due to the presence of
calcium oxide in the snail shell which is in
maximum quantity in cement.
Snail shells are waste products which are obtained
from the consumption of snails. Snail shells are
very strong, hard and brittle material. The snails
found in lagoons and mudflats of coastal areas are
consumed by the people as food and the shell is
disposed of as waste product. Large amount of
snail shells are disposed of as waste in these areas,
and the disposal already constitute a problem in
such areas because they cannot find any use for it.
Thus, large deposits have accumulated in the areas
over the years (Zaid and Ghorpade, 2014).
The shell of the large land snail is brownish yellow
in color with dark markings and is up to 10 cm or
more in length; it is very hard. Snail shell has
several important uses, which results from the hard
nature of the shell. The shell protects the snail from
physical damage, predators and dehydration (Jatto
et al, 2010). Snail shells are made of mostly
calcium carbonate. They also contain small
amounts of protein. Fundamentally, the shell
consists of calcium carbonate crystals organised
within a matrix of protein. Calcium carbonate
crystallizes in two principal forms, aragonite and
calcite within the shell. The form present in a
particular shell may depend on several factors. For
example, the crystal type in the shell of the land
snail Helix pomatia is normally aragonite, whiles
the shells of many marine snails and bivalves
normally contain calcite.
Rice husk is waste left behind after the grain of rice
is taken. Rice husk ash is the ash obtained from the
combustion of rice husk and this ash contains high
amount of SiO2 which is a major component of
cement. These waste materials are not properly
handled and are discharged into the environment
which later causes environmental pollution. Rice
Husk and Snail Shell have great potential to be
used as building materials. The combination of
high silica content from RHA, and CaO from the
CSS has pozzolanic behaviour which influences the
concrete strength.
Research has been done on the utilisation of
various forms of CSS and RHA separately in
replacing cement (Abalaka 2012; Abalaka et al.,
2007; Habeeb and Mahmud, 2010; Kartini, 2011;
Zaid and Ghorpade, 2014) but little or no work on
the combination of the two exists in the literature.
Therefore this investigation seeks to determine the
effects of partial replacement of cement with
(Calcined Snail shell, CSS + Rice Husk Ash, RHA)
on the formation of building blocks to ensure
sustainable blocks production, save energy and
make the environment friendlier.
2 Resources and Method Used
2.1 Materials
The snail shells (SS) (Fig. 1) used in this test were
collected from Manso Amenfi in the Western
Region of Ghana whilst the Rice husk (RH) (Fig.
2) was collected from Hohoe in the Volta Region
of Ghana. Fine aggregates of sand and Ordinary
Portland Cement (OPC, GHACEM Brand) were
obtained from Tandoh and Sons Solid Rock Block
Enterprise.
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GGJJTT Vol. 1, No. 1, September, 2016
Fig. 1 Sample of Snail Shell utilised for the
Investigation
Fig. 2 Samples of Rice Husk utilised for the
Investigation
2.1.1 Preparation and Blending of Materials
The rice husk sample was dried. The sample was
burned in an evaporating dish on a gas fired
furnace at a temperature of about 800 °C. After
about 4 hours the sample in the dish completely
turned ash. The ash was allowed to cool and
screened. A screen of aperture size 90 micron was
used in the screening process. After screening, both
the oversize and undersize rice husk sample were
bagged.
The land snail collected was washed to remove
impurities. The sample was dried and calcined at
above 700 ºC in a furnace. After calcination, the
shells were crushed using a lab size jaw and roll
crushers at the Minerals Engineering laboratory of
UMaT. The sample was further milled by using a
laboratory size ball mill. The milled sample was
screened using a screen of aperture size 90
microns.
2.1.2 Characterisation of Materials
The experimental materials (CSS, RHA and OPC)
were characterised by XRF and XRD and the
morphology of pulverised samples were observed
using SEM analyses.
2.2 Mixing and Moulding
A mould of size 100 mm × 70 mm × 50 mm (Fig.
3) was used for casting all blocks. The overall
sample mass for sand, cement, rice husk ash and
calcined snail shell used for forming the blocks are
16.80 kg, 7.54 kg, 0.43 kg and 1.72 kg
respectively. A ratio of 1: 3 of sand to cement was
used. A blend of 20 % of RHA and 80 % of CSS
was the mixture of the cementitious material used
as replacement for forming blocks. The percentage
replacement used are 0 %, 5 %, 10 %, 15 %, 20 %,
25 %, 30 % and 50 %. The 0 % replacement was
used as the control sample. The quantities of
materials obtained from the mix design were
measured in each case with the aid of an electronic
balance. The particle size of the sand used is
oversize of 0.56 mm. Details of the cast blocks are
shown in Table 1.
Fig. 3 The Mould used for the Investigation
The mixture was mixed thoroughly by means of a
trowel to obtain homogenous mixture. Water was
sprinkled on the mixture.
Table 1 Percent Replacement and their
Respective Masses of Raw Materials
%Replacement Mass of Material (g)
Sand Cement RHA CSS
0 2400 1383.20 0 0
5 2400 1314.04 13.83 55.33
10 2400 1244.88 27.68 110.66
15 2400 1175.72 41.49 165.98
20 2400 1106.56 55.32 221.31
25 2400 1037.40 69.16 276.64
30 2400 968.24 82.99 331.97
50 2400 691.60 138.32 553.28
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GGJJTT Vol. 1, No. 1, September, 2016
2.3 Casting and Curing
The uniform mixture which was slightly wet was
then transferred into the mould to cast the block
(Fig. 4). A total of 24 blocks were cast. After each
block was cast, small amount of water was
sprinkled into the metal mould to avoid the block
sticking onto its walls. Curing was performed after
24 hours after casting the blocks. Samples of the
Control and experimentally cast blocks are shown
in Fig. 5 and Fig. 6, respectively.
Fig. 4 Mould filled to the Brim
Fig. 5 Control Block Samples
Fig. 6 Cast Blocks Samples
2.4 Testing Procedure
Compressive test was carried out to determine the
effect of the admixture on the strength of the
blocks. After casting and the samples were air dried
until the testing ages of 7 and 14 days. The
compressive strength was determined with
CONTEST Compressive Strength Testing Machine
(Type GDIOA, Serial Number 3688), Fig. 7, with
maximum capacity of 2000 kN. The test was
carried out in the Geological Department
Laboratory, University of Mines and Technology,
Tarkwa.
Fig. 7 Compressive Test Machine
3 Results and Discussion
3.1 Characterisation of Materials
3.1.1 XRF Analyses of RHA, CSS and Cement
The XRF analyses of the samples are illustrated in
Table 2. It is apparent from Table 2 that whereas
RHA is dominated by SiO2 with negligible amount
of CaO (< 1%), CSS is dominated by CaO with
negligible amount of SiO2 (< 1%). Accordingly,
suitable blends of RHA and CSS should be able to
conveniently replace cement in building blocks,
since cement contains reasonable amounts of both
CaO and SiO2. To ensure that the content of CaO
will be higher than that of SiO2, the ratio of RHA:
CSS in the replacing blend was set at 4:1. Table 2
gives an LOI of 43.08%. This value is inclusive of
the CO2 that was expelled from CSS during the
calcination process.
Table 2 Chemical Analyses (XRF) of Samples
utilised for the Investigation Component CSS
(wt %)
RHA
(wt %)
Cement (wt
%)
CaO 57.92 0.75 53.43
SiO2 0.82 85.77 21.62
Al2O3 0.14 0.28 4.80 Fe2O3 0.22 0.30 3.04
K2O 0.06 3.90 0.68
SO3 0.01 0.37 2.56 Na2O 0. 06 0.26 0.58
MgO <0.01 1.50 3.41
LOI 43.08* 2.34 9.40
*LOI includes expelled CO2 from calcination of SS
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GGJJTT Vol. 1, No. 1, September, 2016
3.1.2 XRD Analyses of RHA, CSS and Cement
The XRDs are shown in Figs. 8, 9 and 10 for CSS,
RHA and cement, respectively. It is seen from the
XRDs that Snail shell is crystalline and is
dominated by sharp and well-defined peaks of
calcite (CaCO3). RHA is, however, amorphous and
its XRD consists of amorphous SiO2. The XRD of
cement, as illustrated in Fig. 9, consists of peaks
three distinct compounds, viz., SiO2, Ca2SiO4 and
Ca3SiO5.
Fig. 8 XRD Patterns of Sea Shells showing Peaks
of Calcite (CaCO3)
Fig. 9 XRD Patterns of RHA showing
Amorphous Peaks of SiO2
Fig. 10 XRD Patterns of OPC
3.1.3 SEM Analyses of RHA, CSS and Cement
The SEM photomicrographs of SS, CSS, RHA and
OPC are shown in Figs (11, 12, 13 and 14),
respectively. The SEM of the pulverised SS
consists of well-defined tubular structures whereas
interspersed between irregularly shaped and
irregularly sized structures.
Fig. 11 SEM Photomicrographs of Pulverised
Snail Shells Utilised for the Investigation
Calcination of the SS results in more uniform
spherically shaped structures as displayed in Fig.
11. The SEM photomicrographs of RHA and OPC
show structures that are irregularly shaped.
Fig. 12 SEM Photomicrographs of Calcined
Snail Shells Utilised for the Investigation
Fig. 13 SEM Photomicrographs of RHA Utilised
for the Investigation
0
2000
4000
6000
8000
10000
12000
10 20 30 40 50 60 70 80
Inte
nsi
ty (
Arb
itra
ry U
nit
s)
Position [°2θ] [Cobalt (Co)]
1
1
1 1, 2
2 1 1 1
1 1 1
1 Calcite, syn
2 Silica, syn
3 Aragonite, syn
0
400
800
1200
1600
2000
10 20 30 40 50 60 70 80
Inte
nsi
ty (
Arb
itra
ry U
nit
s)
Position [°2θ] {Cobalt (Co)}
SiO
2
SiO
2
SiO
2
0
400
800
1200
1600
2000
10 20 30 40 50 60 70 80
Inte
nsi
ty (
Arb
itra
ry U
nit
s)
Position {°2θ} (Cobalt {Co})
1 SiO2
2 Ca2.SiO4
3 Ca3SiO5
1
1 3
1
3
3
2
2, 3
2, 3
1, 2, 3
3 1
, 2,
3
2, 3
2, 3
1, 3
2 1,
3
3
3 1, 3
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GGJJTT Vol. 1, No. 1, September, 2016
Fig. 14 SEM Photomicrographs of OPC Utilised
for the Investigation
3.3 Compressive Strength
The stages involved in the measurement of the
compressive strengths of the blocks are illustrated
in Fig. 15.
Fig. 15 Various Stages during Testing. (a) Initial
stage, (b) Compression stage and (c) Final
stage
The effect of curing ages on the compressive
strength of building block is presented in Table 3.
Table 3 indicates that compressive strength
generally increases with curing age and decreases
with increased amount of pozzolanic materials
added. The results at 14th day showed a percentage
increase of 6.15 %, 10.6 %, 88.36 % and 27.45 %
for control (0 %), 20 %, 25 % and 30 % partial
cement replacement, respectively from the 7th day.
However, there was a decrease in compressive
strength for the 5 %, 10 %, 15 % and 50%
replacement with values 33.57 %, 14.71 %, 19.57
%, 10.6 4%, 26.26 % respectively.
The results at 14th
day indicated that pozzolanic
action had commenced as evident from the higher
percentage increase in compressive strength by the
20 %., 25 % and 30% replacement. However, the
control still had the highest compressive strength at
this age. But the 25 % replacement gave the highest
percentage increase in compressive strength. The
result can be attributed to the right requirement of
the silica in the block formed in the 20 %., 25 %
and 30% replacement to react with water during the
hydration of cement to increase the compressive
strength. This then confirms the observation by
Oyetola and Abdullahi (2006) that for lower
percentage replacement level of 10 % and 20 %
RHA the silica from the pozzolana is in the
required amount, which aids the hydration process
to produce blocks with high compressive strength.
Therefore 20 %, 25 % and 30 % had right
requirement of silica in the blocks formed.
A high value of 88.36 % increase of strength from
the 7th
day to the 14th
day was obtained for building
block with 25 % replacement of RHA and CSS.
Therefore it is the optimum partial percentage
replacement for forming blocks. All the blocks
formed meet the minimum strength of 3.5
N/ for a standard block (Oyetola and
Abdullahi, 2006b) for all ages.
It must be mentioned here that blocks were
produced without chemical activation.
Accordingly, strength development appears to be
generally slow and irregular. Further work is
ongoing aimed at the influence of chemical
activation agents on compressive strength
development in a bid towards sustainable
production of affordable building blocks
production.
Table 3 Weight, Load and Compressive Stress of the Blocks
7 Days 14 Days
% Replacement Weight (g) Load (kN) Stress (MPa) Weight (g) Load (kN) Stress (MPa)
0 715 59.53 12.52 712.30 63.75 13.29
5 694 60.10 12.78 677.00 40.30 8.49
10 686.50 54.10 11.15 670.00 48.50 9.51
15 680.60 37.60 7.51 665.90 29.00 6.04
20 673.60 43.30 8.65 653.20 46.90 9.37
25 658.40 28.60 5.67 642.30 51.02 10.68
30 649.80 40.00 8.16 636.20 50.50 10.40
50 639.50 27.40 5.56 628.50 25.40 4.10
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GGJJTT Vol. 1, No. 1, September, 2016
4 Conclusions
From this work it can be concluded that:
(i) RHA and CSS can be used as partial
replacement for cement in building blocks
production.
(ii) The compressive strength of the blocks
generally increases with age at curing but
decreases as the content of RHA and CSS
increases.
(iii) All the building blocks produced had
compressive strength higher than the
minimum required strength of 3.5 N/
for a standard block.
(iv) The optimum addition of RHA and CSS as
partial replacement for cement to form
building blocks is 25%.
Acknowledgements
Part of the analyses for the investigation was
conducted at the School of Materials Science and
Engineering and the Analytical Centre, School of
Chemical Science and Engineering, UNSW,
Sydney, Australia. The authors are grateful to the
various authorising bodies for the assistance
received.
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Authors Ebenezer Nkrumah obtained his BSc degree in Minerals Engineering from the
University of Mines and Technology,
(UMaT) Tarkwa, Ghana. He is part of the Sustainable Materials Research Group of
the Minerals Engineering Department,
UMaT, Tarkwa, Ghana. His research areas include the blending of materials into useful products.
James R. Dankwah is a Senior Lecturer at
the University of Mines and Technology (UMaT) Tarkwa. He holds his PhD from
the School of Materials Science and
Engineering, UNSW, Australia, MSc (Process Metallurgy) from the Norwegian
University of Science and Technology and
BSc (Metallurgical Engineering) from the Kwame Nkrumah University of Science and Technology,
Kumasi, Ghana. His current research areas include iron and
steelmaking, high-temperature metallurgical processes, utilisation of waste polymers in metal extraction processes and
recycling agricultural waste into building blocks materials for
affordable housing for rural folks.